U.S. patent application number 16/967075 was filed with the patent office on 2021-02-18 for method for determining section in which generation of internal gas in second battery accelerates.
This patent application is currently assigned to LG CHEM, LTD.. The applicant listed for this patent is LG CHEM, LTD.. Invention is credited to Dong Guk HWANG, Su Hyun KIM, Ji Hye PARK.
Application Number | 20210048481 16/967075 |
Document ID | / |
Family ID | 1000005236019 |
Filed Date | 2021-02-18 |
United States Patent
Application |
20210048481 |
Kind Code |
A1 |
PARK; Ji Hye ; et
al. |
February 18, 2021 |
METHOD FOR DETERMINING SECTION IN WHICH GENERATION OF INTERNAL GAS
IN SECOND BATTERY ACCELERATES
Abstract
The present invention relates to a method for determining a
section in which generation of internal gas in a second battery
accelerates, the method comprising the steps of: measuring a closed
circuit voltage (CCV) and an open circuit voltage (OCV) according
to the state of charge (SOC) of the secondary battery while
charging the secondary battery; deriving a closed circuit voltage
(SOC-CCV) profile according to the state of charge and an open
circuit voltage (SOC-OCV) profile according to the state of charge;
and determining, from the derived SOC-CCV profile and SOC-OCV
profile, a section in which the amount of internal gas generated in
the secondary battery rapidly increases.
Inventors: |
PARK; Ji Hye; (Daejeon,
KR) ; KIM; Su Hyun; (Daejeon, KR) ; HWANG;
Dong Guk; (Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG CHEM, LTD. |
Seoul |
|
KR |
|
|
Assignee: |
LG CHEM, LTD.
Seoul
KR
|
Family ID: |
1000005236019 |
Appl. No.: |
16/967075 |
Filed: |
September 30, 2019 |
PCT Filed: |
September 30, 2019 |
PCT NO: |
PCT/KR2019/012707 |
371 Date: |
August 3, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 31/392 20190101;
H01M 10/44 20130101; H01M 10/48 20130101; H02J 7/0048 20200101;
H02J 7/0013 20130101; H02J 7/00719 20200101; G01R 31/396
20190101 |
International
Class: |
G01R 31/392 20060101
G01R031/392; H01M 10/44 20060101 H01M010/44; H01M 10/48 20060101
H01M010/48; H02J 7/00 20060101 H02J007/00; G01R 31/396 20060101
G01R031/396 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2018 |
KR |
10-2018-0128396 |
Claims
1. A method for determining an internal gas generation acceleration
section of a secondary battery, the method comprising: measuring a
closed circuit voltage (CCV) and an open circuit voltage (OCV)
according to a charge amount (SOC) of the secondary battery while
charging the secondary battery; deriving a closed circuit voltage
profile (SOC-CCV profile) according to the charge amount and an
open circuit voltage profile (SOC-OCV profile) according to the
charge amount; and determining a section in which an internal gas
generation amount of the secondary battery is rapidly increased
from the SOC-CCV profile and the SOC-OCV profile.
2. The method of claim 1, wherein in the SOC-CCV profile, a
section, in which the closed circuit voltage is continuously
increased and a slope of the SOC-OCV profile is decreased, is
determined as the section in which the gas generation amount is
rapidly increased.
3. The method of claim 2, wherein the section in which the gas
generation amount increases rapidly is a charge amount section in
which a slope of the SOC-CCV profile is the same as or increased
compared to a slope of the SOC-CCV profile of a previous section,
and the slope of the SOC-CCV profile decreases in a subsequent
section.
4. The method of claim 3, wherein the section in which the gas
generation amount increases rapidly is a charge amount section in
which the slope of the SOC-CCV profile increases more than 1.2
times compared to the previous section.
5. The method of claim 2, wherein in the section in which the gas
generation amount increases rapidly, a slope change rate of the
SOC-OCV profile is less than .+-.5%.
6. The method of claim 2, wherein in the section in which the gas
generation amount increases rapidly, a change value in the open
circuit voltage is .+-.10 to 200 mV.
7. The method of claim 1, wherein the closed circuit voltage and
the open circuit voltage are continuously increased before the
section in which the gas generation amount rapidly increases.
8. The method of claim 1, wherein the secondary battery includes
one or more small cells having a capacity of 1 Ah or less, and the
small cells are electrically connected to each other.
9. The method of claim 8, wherein an internal gas generation
acceleration section for a medium-large cell module is predicted by
charging the small cell under a simulation condition of the
medium-large cell module.
10. The method of claim 9, wherein the simulation condition of the
medium-large cell module is a condition that a front surface of the
small cell is wrapped with a heat insulating member in order to
block a heat leakage to an outside.
11. The method of claim 9, wherein the medium-large cell module
includes one or more medium-large cells having a capacity of 20 Ah
or more.
12. The method of claim 11, wherein the medium-large cell module is
used as a power source for an electric vehicle, a hybrid electric
vehicle, a plug-in hybrid electric vehicle, or a power storage
device.
Description
TECHNICAL FIELD
[0001] This application claims the benefit of priority based on
Korean Patent Application No. 10-2018-0128396, filed on Oct. 25,
2018, and the entire contents of the Korean patent application are
incorporated herein by reference.
[0002] The present invention relates to a method for determining a
section in which the amount of gas generated internally at the time
of ignition or explosion due to overcharging of a secondary battery
increases rapidly.
BACKGROUND ART
[0003] Recently, secondary batteries capable of charging and
discharging have been widely used as energy sources of wireless
mobile devices. In addition, the secondary battery has attracted
attention as an energy source of an electric vehicle, a hybrid
electric vehicle, etc., which are proposed as a solution for air
pollution of existing gasoline vehicles and diesel vehicles using
fossil fuel.
[0004] Small devices such as mobile phones and cameras use small
battery packs packed with one secondary battery cell, whereas
medium and large devices such as laptops and electric vehicles use
medium or large battery packs in which two or more secondary
battery cells are connected in parallel and/or in series.
[0005] Such secondary batteries may be classified into lithium ion
batteries, lithium ion polymer batteries, lithium polymer
batteries, etc., depending on the composition of the electrode and
the electrolyte, and among them, the amount of use of lithium-ion
polymer batteries that are less likely to leak electrolyte and are
easy to manufacture is on the increase.
[0006] On the other hand, the lithium secondary battery has a
problem of low safety while having excellent electrical properties.
For example, lithium secondary batteries generate heat and gas due
to decomposition reaction of active materials and electrolytes,
which are battery components, under abnormal operating conditions
such as overcharge, overdischarge, exposure to high temperatures,
and electrical short circuits, and the resistance of the battery
increases and gas generation is accelerated, which may cause
ignition or explosion.
[0007] In addition, the safety problem of the secondary battery is
more serious in the medium-large cell module of the multi-cell
structure. It is because a large number of battery cells are used
in a cell module having a multi-cell structure, so that an abnormal
operation in some battery cells may cause a chain reaction to other
battery cells, and ignition and explosion due thereto may result in
large accidents.
[0008] Accordingly, the necessity for safety evaluation due to
overcharging, high temperature exposure, etc. of the secondary
battery is increasing. In particular, there is a need for measuring
a sudden increase time of gas generated inside the secondary
battery. However, the explosion of the medium and large cell module
is not only a risk that can be caused by a large accident by the
chain reaction as described above, but also due to the structural
deformation of the measuring device, it is difficult to measure the
time of sudden increase of gas, etc.
[0009] As such, there is a demand for a method for measuring an
acceleration time point of generation of gas generated therein due
to overcharging when evaluating the safety of secondary
batteries.
DISCLOSURE
Technical Problem
[0010] An object of the present invention is to provide a method of
determining a gas generation acceleration section, that is, a
section in which the amount of gas is rapidly increased, without
actually analyzing the gas generated inside the secondary
battery.
Technical Solution
[0011] A method for determining an internal gas generation
acceleration section of a secondary battery according to an
embodiment of the present invention includes: measuring a closed
circuit voltage (CCV) and an open circuit voltage (OCV) according
to a charge amount (SOC) of the secondary battery while charging
the secondary battery; deriving the closed circuit voltage
(SOC-CCV) profile according to the charge amount and the open
circuit voltage (SOC-OCV) profile according to the charge amount;
and determining a section in which an internal gas generation
amount of the secondary battery is rapidly increased from the
derived SOC-CCV profile and SOC-OCV profile.
[0012] Herein, in the SOC-CCV profile, a section, in which the
closed circuit voltage is continuously increased and a slope of the
SOC-OCV profile is decreased, may be determined as a section in
which the gas generation amount is rapidly increased.
[0013] In an embodiment of the present invention, the section in
which the gas generation amount increases rapidly may be a charge
amount section in which the slope of the SOC-CCV profile is the
same or increased compared to the previous section, and the slope
may decrease in a subsequent section.
[0014] In an embodiment of the present invention, the section in
which the gas generation amount increases rapidly may be a charge
amount section in which the slope of the SOC-CCV profile increases
more than 1.2 times compared to the previous section.
[0015] In an embodiment of the present invention, in the section in
which the gas generation amount increases rapidly, a slope change
rate of the SOC-OCV profile may be less than .+-.5%.
[0016] In an embodiment of the present invention, in the section in
which the gas generation amount is rapidly increased, the change
value of the open circuit voltage may be .+-.10-200 mV.
[0017] In an embodiment of the present invention, the closed
circuit voltage and the open circuit voltage may be continuously
increased before the section in which the gas generation amount
rapidly increases.
[0018] In an embodiment of the present invention, the secondary
battery may include one or more small cells having a capacity of 1
Ah or less, and the small cells may be electrically connected to
each other.
[0019] In an embodiment of the present invention, an internal gas
generation acceleration section for a medium-large cell module may
be predicted by charging the small cell under a simulation
condition of the medium-large cell module.
[0020] In an embodiment of the present invention, the simulation
condition of the medium-large cell module may be a condition that a
front surface of the small cell is wrapped with a heat insulating
member in order to block a heat leakage to an outside.
[0021] In one embodiment of the present invention, the medium-large
cell module may include one or more medium-large cells having a
capacity of 20 Ah or more.
[0022] The medium-large cell module may be used as a power source
for an electric vehicle, a hybrid electric vehicle, a plug-in
hybrid electric vehicle, or a power storage device.
Advantageous Effects
[0023] According to an exemplary embodiment of the present
invention, the internal gas generation acceleration section may be
determined only by the profile of the closed circuit voltage and
the open circuit voltage according to the charge amount, without
actually analyzing gases generated at the time of ignition due to
the overcharging of the secondary battery. This eliminates the need
for a separate gas analysis device, thereby reducing the safety
test cost of the secondary battery.
[0024] In addition, various improvement methods, such as gas
removal and exhaust system, may be easily applied based on the
generation acceleration section. Further, since the gas generation
acceleration section can be confirmed only by the voltage profile,
the gas generation acceleration section can be confirmed regardless
of the material of the active material and the capacity of the
secondary battery.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a flowchart schematically illustrating a method of
determining an internal gas generation acceleration section of a
secondary battery according to an embodiment of the present
invention.
[0026] FIG. 2 schematically illustrates an SOC-OCV profile and an
SOC-CCV profile for determining a gas generation acceleration
section.
[0027] FIGS. 3 and 4 show SOC-OCV profiles and SOC-CCV profiles
according to Examples 1 and 2, respectively.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] As the inventive concept allows for various changes and
numerous embodiments, particular embodiments will be illustrated in
the drawings and described in detail in the text. However, this is
not intended to limit the present invention to the specific form
disclosed, and it should be understood to include all changes,
equivalents, and substitutes included in the spirit and scope of
the present invention.
[0029] In describing the drawings, similar reference numerals are
used for similar elements. In the accompanying drawings, the
dimensions of the structures are shown in an enlarged scale for
clarity of the invention. Terms such as "first" and "second" may be
used to describe various components, but the components should not
be limited by the terms. The terms are used only for the purpose of
distinguishing one component from another. For example, without
departing from the scope of the present invention, a first
component may be referred to as a second component, and similarly,
the second component may also be referred to as the first
component. Singular expressions include plural expressions unless
the context clearly indicates otherwise.
[0030] In this application, it should be understood that terms such
as "include" or "have" are intended to indicate that there is a
feature, number, step, operation, component, part, or a combination
thereof described on the specification, and they do not exclude in
advance the possibility of the presence or addition of one or more
other features or numbers, steps, operations, components, parts or
combinations thereof. Also, when a portion such as a layer, a film,
an area, a plate, etc. is referred to as being "on" another
portion, this includes not only the case where the portion is
"directly on" the another portion but also the case where further
another portion is interposed therebetween. On the other hand, when
a portion such as a layer, a film, an area, a plate, etc. is
referred to as being "under" another portion, this includes not
only the case where the portion is "directly under" the another
portion but also the case where further another portion is
interposed therebetween. In addition, to be disposed "on" in the
present application may include the case disposed at the bottom as
well as the top.
[0031] Hereinafter, a method of determining an internal gas
generation acceleration section of a secondary battery according to
an embodiment of the present invention will be described with
reference to the drawings.
[0032] FIG. 1 is a flowchart schematically illustrating a method of
determining an internal gas generation acceleration section of a
secondary battery according to an embodiment of the present
invention, and FIG. 2 schematically illustrates an SOC-OCV profile
and an SOC-CCV profile for determining a gas generation
acceleration section.
[0033] A method for determining an internal gas generation
acceleration section of a secondary battery according to an
embodiment of the present invention includes: measuring a closed
circuit voltage (CCV) and an open circuit voltage (OCV) according
to a charge amount (SOC) of the secondary battery while charging
the secondary battery (S100); deriving the closed circuit voltage
(SOC-CCV) profile according to the charge amount and the open
circuit voltage (SOC-OCV) profile according to the charge amount
(S200); and determining a section in which an internal gas
generation amount of the secondary battery is rapidly increased
from the derived SOC-CCV profile and SOC-OCV profile (S300).
[0034] First, while charging the secondary battery, the step (S100)
of measuring the closed circuit voltage (CCV) and the open circuit
voltage (OCV) according to the charge amount (SOC) of the secondary
battery may be measuring the closed circuit voltage (CCV) and open
circuit voltage (OCV) according to the charge amount while charging
the secondary batteries and, at the same time, inducing gas
generation of secondary batteries while continually increasing the
charge amount.
[0035] The secondary battery may generate heat and gas by causing
decomposition reactions of active materials, electrolytes, and the
like, which are battery components, by overcharge, and the high
temperature and high pressure conditions caused by the secondary
battery may further accelerate the decomposition reaction and cause
fire or explosion. Since the present invention is to determine a
charge amount section in which the gas generation amount is rapidly
increased during the safety test, the charge amount (SOC) of the
secondary battery is continuously increased by continuously
applying a charging current to the secondary battery to be
inspected to induce gas generation.
[0036] In this case, by applying a charging current by using 200%
limit of the charge amount SOC, an explosion of the secondary
battery may be induced, but the present invention is not limited
thereto, and overcharging may be performed until the secondary
battery is exploded. As described above, the overcharge may be
performed after limiting the upper limit voltage to about twice the
operating voltage without using the charge amount as the reference
value.
[0037] On the other hand, overcharging may be performed through a
charge/discharge unit disposed on one side of the chamber after
mounting the secondary battery in the chamber of the analysis
device. The chamber may include a chamber body and a chamber cover,
and the chamber body may have a hollow structure with an open top.
In addition, the shape and size of the chamber body on the plane
are not limited and may have a cube shape or a cuboid shape as a
shape and size of the secondary battery mounted therein. The
chamber cover may be coupled with an opening of the chamber body in
order to seal a secondary battery mounted inside the chamber body.
The chamber body and the chamber cover are not particularly limited
as long as the chamber body and the chamber cover can be firmly
coupled, but may be coupled by fixing means such as fixing pins,
screws, and bolts. In addition, an O-ring or the like may be
further used between the chamber body and the chamber cover in
order to increase the coupling force of the chamber body and the
chamber cover. The inner surface of the chamber may be an
insulating and heat-insulating material, and a material resistant
to high temperature and high pressure, and non-limiting examples
thereof may be bakelite, teflon, aerosol, or the like. The outer
surface surrounding the inner surface may be made of a material
such as stainless steel or metal. Meanwhile, the inside of the
chamber may be formed in a vacuum state so as to derive a more
accurate result value.
[0038] In addition, the charge/discharge unit may include a power
supply unit and a measuring unit. The power supply unit may be
electrically connected to the secondary battery mounted through the
charge/discharge terminals. Specifically, charge/discharge
terminals are provided at one side of the chamber, and may be
electrically connected to an electrode of a secondary battery in
which the charge/discharge terminals are mounted.
[0039] The measurement of the closed circuit voltage CCV and the
open circuit voltage OVC according to the charge amount SOC of the
secondary battery may be simultaneously performed while applying a
charging current to the secondary battery to be inspected, but is
not limited thereto. Further, the charging current may be applied
up to a specific charging amount SOC, and the voltage may be
measured after the secondary battery is left.
[0040] In the present invention, the closed circuit voltage is a
voltage of the secondary battery in a state where a current is
applied to the secondary battery, and the open circuit voltage
means a voltage of a secondary battery in a state in which no
current is applied to the secondary battery. The closed circuit
voltage according to the SOC can be measured by measuring the
voltage when reaching a specific SOC while continuously charging,
and the open circuit voltage according to the charge amount of the
secondary battery can be measured by repeating the process of
charging up to a specific charge amount, leaving the battery for at
least one hour and then measuring the voltage. At this time, the
time to leave the secondary battery for measurement of the open
circuit voltage is not limited to the above numerical value.
[0041] In one embodiment of the present invention, the step S100 of
measuring the closed circuit voltage CCV and the open circuit
voltage OCV according to the charge amount SOC may be performed
through the above-described measuring unit. Accordingly, the
voltage of the secondary battery can be measured in real time while
applying current to the secondary battery. The voltage measured by
the measuring unit may be stored in a separate storage unit, and
the voltage profile described below may be formed using the stored
voltage measurement value.
[0042] The step of deriving the profile of the closed circuit
voltage (CCV) and the open circuit voltage (OCV) according to the
charge amount (SOC) (S200) is a step of forming measured values of
the SOC-CCV according to the measuring step (S100) and a graph
showing the measured values.
[0043] Specifically, as shown in FIG. 2, the SOC-CCV profile and
the SOC-OCV profile can be formed by setting the charge amount SOC
on the horizontal axis and the closed circuit voltage CCV and the
open circuit voltage OCV on the vertical axis, respectively, and
plotting each measurement value on a graph.
[0044] Thereafter, a step S300 of determining a generation
acceleration section of gas generated inside the secondary battery
may be performed based on the behavior of the SOC-CCV profile and
the SOC-OCV profile.
[0045] In particular, according to the method of determining the
generation acceleration section of the gas, a section in which the
closed circuit voltage continuously increases in the SOC-CCV
profile and the slope of the SOC-OCV profile decreases is
determined as a section in which the gas generation amount rapidly
increases.
[0046] Referring to FIG. 2, the closed circuit voltage shows a
tendency to continuously increase as charging progresses, and after
a period of rapid increase in speed, a short occurs due to an
increase in resistance of the secondary battery. At this time, the
gas generation acceleration section (G) may be a charge amount
section in which the closed circuit voltage according to the amount
of charge is continuously increased, or the slope of the SOC-CCV
profile is increased or the same when compared to that of the
previous period (S.sub.1). Thereafter, the slope of the SOC-CCV
profile may be decreased in the following section S.sub.2.
[0047] In an embodiment of the present invention, the gas
generation acceleration section G may be a charging amount section
in which the slope of the SOC-CCV profile is increased by 1.2 times
or more when compared to the acceleration section S.sub.1.
[0048] In addition, a trend that the closed circuit voltage is
continuously increased is shown before the gas generation
acceleration section (S.sub.1), and a trend that the slope of the
closed circuit voltage decreases may be shown thereafter (S.sub.2).
Further, as the overcharging continues, the resistance of the
secondary battery increases, resulting in a short circuit.
[0049] On the other hand, the open circuit voltage shows a tendency
to continuously increase as the overcharge proceeds, it can be seen
that the increase rate is slowed from a certain section. In this
case, the generation acceleration section G of the gas may be a
charging amount section in which the increase rate of the open
circuit voltage is slowed, that is, the slope of the SOC-OCV
profile decreases. In an embodiment of the present invention, the
slope change rate of the SOC-OCV profile may be less than .+-.5%
and the change value .DELTA.V of the open circuit voltage may be
.+-.10 to 200 mV in the gas acceleration section G.
[0050] In addition, before the section in which the generation
amount of gas is rapidly increased (S.sub.1), the closed circuit
voltage and the open circuit voltage may have a trend that
continues to increase, respectively.
[0051] As described above, according to the present invention, in
the SOC-CCV profile and the SOC-OCV profile, a section in which the
slope of the SOC-OCV profile decreases while the closed circuit
voltage is continuously increased is determined as a section in
which the gas generation amount rapidly increases.
[0052] Therefore, in the present invention, the internal gas
generation acceleration section may be determined only by the
profile of the closed circuit voltage and the open circuit voltage
according to the charging amount, without substantially analyzing
the gas generated at the time of the ignition due to the
overcharging of the secondary battery. This eliminates the need for
a separate gas analysis device, thereby reducing the cost of safety
testing the secondary battery.
[0053] In addition, various improvement methods, such as gas
removal and exhaust system at the time of the overcharge of the
secondary battery, may be easily applied based on the acceleration
section of gas generation. In addition, since the gas generation
acceleration section can be confirmed only by the voltage profile,
the gas generation acceleration section can be confirmed regardless
of the material of the active material and the capacity of the
secondary battery.
[0054] Meanwhile, secondary batteries used in the present invention
may include one or more small cells each having a capacity of 1 Ah
or less, and the small cells may be electrically connected to each
other. The small cell is used in a small device such as a mobile
phone, a camera, and the like, and there is no limitation in the
appearance of the cell, but the cell may be a cylindrical, square,
pouch, coin type, or the like using a can.
[0055] According to the present invention, the internal gas
generation acceleration section for the medium-large cell module
can be predicted using small cells.
[0056] In general, a large number of battery cells are used in a
medium-large cell module having a multi-cell structure, so that an
abnormal operation in some battery cells may cause a chain reaction
to other battery cells, and ignition and explosion due thereto may
result in large accidents. Accordingly, the necessity for safety
evaluation due to overcharging, high temperature exposure, etc. of
the medium-large cell module is increasing. In particular, there is
a need for measuring a sudden increase time of gas generated inside
the medium-large cell module due to overcharging. However, the
explosion of the medium and large cell module is not only a risk
that can be caused by a large accident by the chain reaction as
described above, but also due to the structural deformation of the
measuring device, it is difficult to measure the time of sudden
increase of gas, etc.
[0057] Accordingly, the present invention proposes a method of
predicting an internal gas generation acceleration section for a
medium-large cell module by charging a small cell under simulated
conditions of the medium-large cell module without directly testing
the medium-large cell module.
[0058] In general, when a small cell performs a simple overcharge,
the voltage and temperature according to the charge amount tend to
be different compared to that of the medium-large cell module, and
the explosion does not occur even after the charge point at which
the medium-large cell module explodes. This is because the
temperature of the battery does not increase rapidly even if the
decomposition reaction of the electrolyte occurs due to
overcharging in the small cell. On the other hand, in the case of
the medium-large cell module, the battery temperature rises rapidly
due to overcharging.
[0059] Thus, in the present invention, in the process of charging
the small cell, in order to simulate the medium-large module, the
front surface of the small cell to be examined is characterized in
that it is wrapped with a heat insulating member. Thus, charging is
performed after the front surface of the small cell is wrapped with
insulation, so that when overcharged, the calorific value does not
leak to the outside of the battery, thereby accelerating the
temperature rise of the small cell and becoming the same as the
voltage and temperature profile according to the charge amount of
the medium-large cell module.
[0060] At this time, non-limiting examples of the insulating member
include at least one of glasswool, EPS (Expanded Polystyrene), XPS
(Extruded Polystyrene Sheet), polyurethane foam, aqueous flexible
foam, urea foam (Urea Foam), vacuum insulation panel, PVC, and heat
reflective insulation, but any material that can be retained in the
internal space without exiting the heat generated by the
overcharging of the secondary battery to the external space may be
used without particular limitation.
[0061] One or more above-described small cells are included, and
the small cells are electrically connected. By performing the gas
generation acceleration section determination method according to
the present invention by allowing the insulating member to surround
the front surface of the secondary battery to be inspected, the gas
generation acceleration section of the medium-large cell module may
be determined.
[0062] Meanwhile, the medium-large cell module is used in
medium-large devices such as notebooks and electric vehicles, and
one or more medium-large cells having a capacity of 20 Ah or more
may be connected in parallel and/or in series. The medium-large
cell module may be used as a power source of an electric vehicle, a
hybrid electric vehicle, a plug-in hybrid electric vehicle, or a
power storage device.
[0063] Hereinafter, the present invention will be described in
detail with reference to Examples, but the following Examples are
merely to illustrate the present invention, and the present
invention is not limited by the following Examples.
Example 1
[0064] After connecting three small cells (1 Ah) containing
Li(Ni.sub.0.6Co.sub.0.2Mn.sub.0.2)O.sub.2(NMC 622) as a positive
electrode active material in series, the front surface was wrapped
with a heat insulating material to prepare a test target battery.
While the charging current was applied to the battery to be
inspected, the open circuit voltage according to the charging
amount and the closed circuit voltage according to the charging
amount were measured, respectively. The measured values were
plotted to obtain an SOC-OCV profile and an SOC-CCV profile, which
are shown in FIG. 3. Further, in FIG. 3, the section G, in which
the slope of the SOC-OCV profile decreases (the rate of increase of
the OCV slowed down) while the CCV continuously increases or the
CCV rapidly increases (the slope of the SOC-CCV profile increases),
was determined as a section in which the gas generation amount
rapidly increases.
Example 2
[0065] A SOC-OCV profile and a SOC-CCV profile were obtained in the
same manner as in Example 1, except that
Li(Ni.sub.0.8Co.sub.0.1Mn.sub.0.1)O.sub.2(NMC 811) was used as the
positive electrode active material of the small cell, which is
shown in FIG. 4. Further, in FIG. 4, the section G, in which the
increase rate of OCV is slowed or the change value .DELTA.V of the
OCV is 100 mV or less while the slope of the SOC-CCV profile is
slightly increased or the same compared to the previous section,
was determined as the section where the gas generation amount
rapidly increases.
Experimental Example
[0066] After preparing the same battery as the cells to be
inspected in Examples 1 and 2, the charging current was applied to
measure the ionic strength of the gas according to the charging
amount in real time. These are shown in FIGS. 3 and 4,
respectively.
[0067] Referring to FIGS. 3 and 4, although the material of the
positive electrode active material is different, it can be seen
that the increase rate of the closed circuit voltage according to
the charging amount in the section G is high, and the increase rate
of the open circuit voltage is lowered.
[0068] More specifically, in the case of Example 1, it can be seen
that the slope of the closed circuit voltage in the G section,
which is the gas generation acceleration section, is the same or
increased compared to before the acceleration section (S.sub.1),
and the slope of the open circuit voltage is slightly decreased. In
the case of Example 2, the increase rate of the closed circuit
voltage is same or slightly increased compared to the previous
section S.sub.1, and the open circuit voltage is slowed or changed
to a decreasing trend, and the change value is about 100 mV or
less.
[0069] On the other hand, in the G section determined as a gas
generation acceleration section by the determination method of the
present invention, it can be seen that the ion concentration of the
gas actually increases rapidly.
[0070] Therefore, the gas acceleration interval determination
method of the present invention may determine the gas generation
acceleration section through the SOC-CCV and SOC-OCV profile even
if the gas generation amount is not actually measured or
analyzed.
[0071] In addition, as the medium-large cell module is simulated
from the small cell in the embodiment, the gas generation
acceleration section of the medium-large cell module is also
expected to be the same.
[0072] As such, in the method according to the present invention,
since a separate gas analysis equipment does not need to be
equipped, the safety test cost of the secondary battery can be
reduced, and based on the gas generation acceleration section, it
may be easy to apply various improvement methods such as gas
removal and exhaust system when the secondary battery is
overcharged. In addition, since the gas generation acceleration
section can be confirmed only by the voltage profile, the gas
generation acceleration section can be confirmed regardless of the
material of the active material and the capacity of the secondary
battery.
[0073] Although the above has been described with reference to a
preferred embodiment of the present invention, it can be understood
that those skilled in the art can make various modifications and
changes to the present invention without departing from the spirit
and scope of the invention as set forth in the claims below.
[0074] Therefore, the technical scope of the present invention
should not be limited to the contents described in the detailed
description of the specification but should be defined by the
claims.
* * * * *